Aerial platforms such as balloons and airplanes provide a unique vantage
point for scientific observation. Balloons can fly one hundred times
closer to the surface of Mars than orbiters and can travel a thousand
times further than rovers in a comparable period, thus providing views
of much broader areas of the surface.

How the Balloons Will Work

Balloons have been flying for decades in Earth's stratosphere, which
has an atmosphere as thin as that on the surface of Mars. Conventional
stratospheric balloons have lifetimes limited to a few days because of
the daily heating and cooling of the balloon. Helium superpressure
balloons, currently under development for the Ultra Long Duration
Balloon (ULDB), will fly more than 100 days and perhaps as long as a
year. Smaller superpressure balloons carrying payloads of only a few
kilograms have already flown for as long as a year.

This technology is now being applied to Mars. The Mars balloon
would be deployed soon after the spacecraft enters the Mars
atmosphere and would be rapidly inflated from a helium tank as the
payload descends beneath a parachute. After inflation is complete,
the parachute and tanks would detach and the balloon and its science
payload would then fly at a nearly constant altitude for both day and
night. The balloon's internal pressure would be higher during the day
than at night, although the balloon volume would remain the same.
Strong, lightweight, leak-proof material is under development to permit
large payloads to be flown on Mars by such a balloon and tests of
balloon deployment in the Earth's atmosphere are underway.
Payloads would include imaging, magnetometers, spectroscopy and
any technique that can benefit from surface proximity.

Another kind of lightweight balloon, called
a solar Montgolfiere, named after the French brothers who flew the first
hot air balloon, does not have to be inflated with a light gas such as
helium. Instead, the balloon deploys upon entering the Martian
atmosphere and an opening at the bottom of the balloon fills up
with Martian "air" while falling to the surface. The balloon
would be quickly heated by the sun and provide buoyancy. The balloon
lifetime is limited to a few hours, because it is only buoyant until the
sun goes down. However, the balloon can then play two roles in
exploration.

Two Important Roles for Balloons

First, the balloon can be used to
provide a soft landing for small payloads on potentially hazardous
terrain. The landing should be slower and more controlled than a
parachute-assisted or rocket landing system. Montgolfieres are
attractive because they are not vulnerable to leaks since leaking "air"
would be quickly replaced and re-heated by the sun. Second, once the
Montgolfiere drops off its payload, the balloon could go back up into
the atmosphere with a small gondola that would perform imaging and
gather other science data for the rest of the day. These images would
show greater detail than orbiters, which are so far above the surface.